Couplings can connect two pipes of the same diameter, or, when needed, can connect pipes of different diameters. Those connecting pipes of different diameters are known as reducing couplings. One of the benefits of schedule 40 PVC couplings is their smooth interior wall. This allows them to connect two pipes without creating a reduction in flow however, when reducing couplings are used, flow is reduced slightly because the diameters of the pipes are different.
Schedule 40 PVC couplings also come with a range of ends. The S couplings have slip spigot or socket ends, while the FPT couplings have female pipe threading to be connected with mail threaded ends. S couplings slip into place and can be used with PVC adhesive to ensure a solid fit. FPT couplings screw on to male-threaded pipes for a secure fit. While adhesive can be used with these, it is not considered a necessity. MPT, or male pipe thread, is also an option with some couplings, but this is more rare. Most couplings have the same ends, but when the project necessitates it, you can find couplings with two different end types.
Because these couplings are made from schedule 40 PVC, they are quite durable. They resist corrosion and can be used indoors and outdoors. As long as the system they are being used on does not have high temperature fluids, schedule 40 PVC couplings are an excellent choice for durable, reliable use.